2. Local area networks (33 marks)
a) Explain why data is divided up into packets in order to be
transmitted across a computer network.
(4)
b) Briefly describe and compare the three approaches of parity bits,
checksums and cyclic redundancy check for detecting transmission
errors in packets of data.
(9)
c) Describe the idea of a singe shared communication medium as
the basis for Local Area Network (LAN) technologies. What are the
advantages of this approach?
(4)
d) Compare and contrast repeaters and bridges as ways of
extending LANs.
(4)
e) Describe the mechanisms of frame filtering that are used by
bridges.
(4)
f) Figure 1 shows a bridge that connects two LAN segments, each
containing three computers. The table lists a sequence of events.
Each event involves one of these computers transmitting a packet
to another. This table also contains a column to summarise the
knowledge that the bridge has accumulated up to that point about
which computers are on which segments. A further column is
included to show on which segments each packet will appear.
Assuming that the packets are transmitted in the order they appear
in the table, write down a completed version of this table.
Figure 1.
Event
(transmission of a
packet)
A sends packet to B
B sends packet to A
C sends packet to D
D sends packet to C
A sends packet to B
F sends packet to D
D sends packet to F
E sends packet to A
Knowledge of bridge
about which
computer on which
segments
Packet appears on
which segments.
(6)
g) Why is the approach of a single shared communication medium
unsuitable for use in Wide Area Networks?
(2)